Wash and halve strawberries. Peel rhubarb, similar to celery, by taking a knife and pulling strings off (if desired). Slice into ½ inch slices (no need to be exact).
In a large bowl, add strawberries, rhubarb, sugar, cornstarch, cinnamon, and ¼ teaspoon salt. Add to a 2 ½-3 quart or similar baking dish.
Topping
Add flour, oats, brown sugar, cinnamon, ½ teaspoon salt, and butter to a medium bowl. Mix well using a pastry cutter or fork. Sprinkle over the fruit filling.
Bake 25-30 minutes, until bubbly on the edges and top is lightly browned. Check if rhubarb is done by poking a fork or knife in the center. If still not ready, check at 3 minute intervals until it is cooked to your liking.
Allow to stand for 15 minutes (or longer) before serving to thicken the fruit mixture.
Serve with ice cream, whipped cream, or whipped topping.
Notes
If butter is chilled, grate butter into the mixture and mix with fingers until crumbly.
If topping starts to brown but the fruit is not cooked, cover loosely with foil or parchment and bake for 5 more minutes.
Double the topping and put half in a zip top bag in the fridge or freezer. It will keep for a couple of weeks. Use for your next fruit crisp!